Conventional leather is formed by tanning animal hides. The tanning process treats an animal hide with a variety of substances to improve and maintain leather's desirable physical characteristics for use in clothing, upholstery, luggage and like applications. The most desirable physical characteristics of tanned leather include appearance, feel, resilience to stretching, longevity, treatability with a variety of surface conditioning finishes and natural drape.
Leather's desirable characteristics are attributed in part to it being a fibrous, semi-porous material made up of an entangled, open matrix of resistant collagen fibers. Collagen fibers make up the majority of leather's composition. Collagen fibers are made up of constituent collagen fibril bundles made up in turn by smaller elongated strands of collagen protein known as collagen fibrils.
Generally, the tanning process is directed toward collagen fibers to fix chemically reactive sites on collagen fibers and to increase intramolecular salt links between adjacent collagen molecules. This links the matrix of resistant collagen fiber bundles, leaving tanned leather pliable, and occupies reactive sites that otherwise would allow leather to degrade and rot. The tanning process likewise removes other compounds from the hide that may be susceptible to degradation and/or perform other functions in the hide. Such compounds may be replaced with other materials.
Obtaining natural leather is problematic due to supply hide having varying qualities, tanning process costs, varying hide costs over time and other challenges.
The leather harvesting, tanning and preparation process produces waste leather byproducts in leather scraps and shavings. If not otherwise used, the waste leather is disposed of by landfill or incineration, creating a negative environmental impact.
Artificial leather products containing waste leather, such as bonded leather, attempt to emulate natural leather. Bonded leather is synthetic leather formed by embedding shredded leather particles into various binding materials. The shredded leather and binding material substance may be applied onto a fabric backing carrier.
Bonded leather type synthetic leathers lack the above-noted desirable characteristics of natural leather. This is due to synthetic leathers lacking the continuous matrix of resistant collagen fiber bundles found in natural leather.
The failure of known artificial and synthetic leathers that contain shredded leather particles is that the individual particles do not physically interact to reproduce or emulate the characteristics of a continuous piece of natural leather having an entangled matrix of resistant collagen fibers. Most notably, artificial and synthetic leathers suffer as lacking desirable tear resistance, drape, flexibility and other esthetic attributes.
In tests applied by a conventional tensometer, artificial and synthetic leather samples of 0.010 to 0.080 inch thickness were subjected to pulling stresses under tension to failure. Measurement of maximum applied force before failure was recorded and calculated as maximum tensile strength PSI measurements ranging generally from about 790 PSI to about 1750 PSI.
Likewise, given the inherently variable makeup of organic animal hides and tanning treatments, the tensile strength qualities of tanned natural leather can vary widely. The tensile strength of representative natural tanned leathers have been found to vary from about 2000 to 3200 PSI depending on leather quality, mechanical treatments and coatings applied to the leather.
Processes for forming other types of formed leather substrates containing shredded and fibrillated collagen leather fibers derived from waste derived leather are known. A challenge with these processes is the inability to achieve acceptable levels of fibril dispersion so that subsequently formed leather substrates have the potential for fibril-to-fibril entanglement.
Another challenge is that wet lap products that are formed mid-process are difficult to dewater and represent a limit to the degree of fibril dispersion which can be achieved in a final leather substrate product. Wet lap may refer to a sheet containing the dispersed fibrils, where particles or fibers are suspended in a fluid (such as a slurry), and the wet lap may be pressed or otherwise manipulated to eliminate or remove at least a portion of that fluid.
The interim wet lap products of these processes also tend to have low wet lap strengths. This presents processing challenges with manipulating interim wet lap products in large-scale production processes using known paper-type processing machines. During transition of the interim wet lap from wire mesh sections of paper-type processing machines, the wet lap tends to break reducing process efficiency and making it very difficult or impossible to produce the end product on a large scale.
Another challenge with prior art processes for forming leather substrates is that required leather particles must be shredded or ground to small sizes and passed through screens having likewise small apertures of approximately 3/32 (0.09375) of an inch in diameter in order to attain desired fibril dispersion and interaction between leather particles. These small grind sizes can slow processing times which reduce process productivity and also limits the ability to achieve some desired physical properties.
Yet another challenge with known processes for forming leather substrates derived from waste leather is the inability to obtain an end product having desired qualities in the outer, presentation surface of an end leather product.
Waste leather that is used in methods of producing a leather substrate may be obtained from different sources including strip waste, cuttings and scraps from the processing of source leather of various grades. Source waste leather may be higher quality full grain or top grain leather obtained from surface or top cuts of animal hide. Alternatively, source waste leather may be lower quality split grain or genuine leather obtained from inner split or bottom cuts of animal hide.
Generally, source waste leather obtained from the surface of animal hide contains leather fibers which provide higher strength and tear-resistance qualities over source leather obtained from the inner portions of animal hide. However, source waste leather derived from full grain or top grain leather often contains the residue of protective coatings and other processing agents which can interfere with the steps of properly processing leather particles, resulting in lumps or non-uniform formation of interim wet lap products as well as lumps on the surface of formed leather substrates. These imperfections can limit the use of source waste leather derived from full grain or top grain leather for the disclosed method.
Thus, there is a need for an improved formed leather product that is created from available waste leather byproducts that reproduces desirable physical characteristics of natural leather. The improved leather product should emulate the collagen fiber matrix that is found in natural leather, have predictable physical characteristics including high tear resistance, desired elastic properties for a range of end applications, and treatability by conventional leather conditioning substances. The process of creating the improved leather product should allow improved de-watering of interim wet lap products and have good wet lap strength to facilitate physically manipulating interim wet lap products. The improved leather product should also have desired qualities in its outer, presentation surface.